The present invention relates to electrode-carrying catheters, and more particularly to an inexpensive and reliable electrode-carrying catheter and a method of making the same.
Electrode-carrying catheters are well known in the medical art and find diagnostic and therapeutic utility in a wide variety of different applications. For example, mapping catheters are used diagnostically to produce a wave function of the heart's electrical impulses so that a doctor can determine proper functioning or fault, and location of the fault, in the heart. Ablative catheters are used therapeutically to destroy tissue in the heart causing tachycardia, utilizing radio frequency current catheter ablation. Such catheters are also used for heart pacing purposes and for analgesia in various parts of the body. Depending upon the particular application for which the catheter is used, it may be desirable for the catheter to carry one or more side electrodes, one or more end electrodes, or a combination thereof. The use of a plurality of smaller electrodes rather than a single large electrode frequently enables superior electrical contact with the tissue, this being a highly desirable factor in connection with mapping catheters in particular.
Electrically conductive wires have never proven to be entirely satisfactory as the electrodes since a functional electrode requires a much larger surface area than can be provided by a flexible wire. Further, unless provisions are made to fix the wire relative to the catheter tubing, it is extremely difficult to ensure that the wire is held in place so as to assure a reliable electrical contact. While a wire could be held in place by use of an electrically conductive adhesive securing the wire to the tubing, it would be extremely difficult to create an electrode by applying an adhesive in a thin layer over a large surface area, as would be necessary to ensure that the electrode layer is flexible.
While a biocompatible conductive paint as an electrode has the advantage of being easily applied in an extremely thin layer to the tubing outer surface by printing techniques, so as to ensure flexibility thereof and cover the wire, there are other problems associated with such conductive paint. While the flexible, thin layer of conductive ink painted on the tubing outer surface forms a good "electrical" connection with the wire, the conductive paint does not form a reliable "physical" connection with the wire, as necessary to ensure that the passage of the catheter through the human body along the guidewire to the proposed working site does not to some degree remove, separate or abrade away the thin layer of conductive paint.
Typically electrode-carrying catheters are made by applying metal strips on the outer side and/or distal (front) surfaces of a flexible tubing of non-conductive plastic, each side strip acting as a side or ring electrode and each distal strip acting as an end electrode. The presence of the metal strips limits the natural flexibility of the tubing so that the catheter is not of high flexibility throughout its entire length, and this presents problems in threading the catheter into the human body over a guidewire since the diminished flexibility may limit the ability of the catheter to conform to the travel path defined by the guidewire, leading to blood vessel trauma. Nonetheless, such catheters carrying ring electrodes are in favor because of the high level of reliability of the electrical connections therein.
The conventional processes for forming ring or metal band electrodes flush with the outer surface of a catheter are arduous, time-consuming and/or require further processing. For example, in one process, metal bands and sleeves therebetween are slipped over the tubing outer surface with the sleeves maintaining the appropriate spacing between adjacent electrodes; this requires the use of additional pieces (namely, the sleeves) and an arduous assembly process. Another process requires the tubing to be stretched to lower the outer diameter thereof, metal bands placed over the stretched tubing and disposed in appropriate spatial relationship, and the tubing then heated and released. The metal bands sink into the heat-softened tubing outer surface as the tubing resumes its original configuration (except where the metal bands are embedded therein). This technique requires additional stretching, heating and cooling steps.
The ring electrodes are commonly 0.040 or 0.080 inch in width and composed of the relatively expensive materials gold or platinum. Where a single catheter contains several ring electrodes, clearly the catheter is a relatively expensive device. Further, any placement of a large number of ring electrodes on the catheter results in a catheter which is stiff and difficult to place, thereby presenting an increased risk of blood vessel perforation. As there is but a single layer of wound wires extending from the proximal end of the catheter to the several ring electrodes, the number of ring electrodes borne by a catheter is strictly limited to 6 or so.
Accordingly, it is an object of the present invention to provide an electrode-carrying catheter which does not utilize ring electrodes.
Another object is to provide in one embodiment such a catheter which provides a large number of side electrodes economically and without stiffening.
A further object is to provide such a catheter which in one embodiment has layers of embedded wound wires.
It is also an object of the present invention to provide such a catheter which is easily and inexpensively manufactured.
It is another object to provide processes for the manufacture of such catheters.